Spontaneous genetic hypertension in the rat and its relationship to reduced ac cochlear potentials: implications for preservation of human hearing

Hypertension facilitates age-related diseases. ~ Is hypertension associated with a wide variety of diseases?~

Hypertension, a disease whose prevalence increases with age, induces pathological conditions of ischemic vascular disorders such as cerebral infarction and myocardial infarction due to accelerated arteriosclerosis and circulatory insufficiency of small arteries and sometimes causes hemorrhagic conditions such as cerebral hemorrhage and ruptured aortic aneurysm. On the other hand, as it is said that aging starts with the blood vessels, impaired blood flow associated with vascular aging is the basis for the development of many pathological conditions, and ischemic changes in target organs associated with vascular disorders result in tissue dysfunction and degeneration, inducing organ hypofunction and dysfunction. Therefore, we hypothesized that hypertension is associated with all age-related vascular diseases, and attempted to review the relationship between hypertension and diseases for which a relationship has not been previously well reported. Following our review, we hope that a collaborative effort to unravel age-related diseases from the perspective of hypertension will be undertaken together with experts in various specialties regarding the relationship of hypertension to all pathological conditions.

Association between high systolic blood pressure and objective hearing impairment among Japanese adults: a facility-based retrospective cohort study

This retrospective longitudinal study examined the association between systolic blood pressure and hearing impairment among 13,187 Japanese individuals (men, 46.5%) aged 20-59 years. The systolic blood pressure of participants was categorized as <120, 120-129, 130-139, 140-149, 150-159, and ≥160 mmHg. Using pure-tone audiometry, hearing impairment at 1 and 4 kHz was defined as hearing thresholds in either ear >30 and >40 dB, respectively. We performed multivariable Cox proportional-hazards regression analysis to examine the association using two multiple-imputation methods (fully conditional specification and Markov chain Monte Carlo). There were 695 and 774 hearing-impairment cases at 1 and 4 kHz, respectively, during ~77,000 person-years of follow-up. Compared with the <120 mmHg group, the hazard ratios (95% confidence intervals) of hearing impairment for the 120-129, 130-139, 140-149, 150-159, and ≥160 mmHg groups after adjustment for age, sex, body mass index, high serum glucose, current smoking, and other potential confounders were 1.35 (1.12-1.63), 1.45 (1.13-1.86), 1.07 (0.73-1.58), 1.91 (1.18-3.07), and 1.81 (1.01-3.25), respectively, at 1 kHz using the first imputation method; 1.36 (1.13-1.63), 1.48 (1.17-1.86), 1.09 (0.76-1.58), 1.99 (1.29-3.06), and 1.92 (1.08-3.41), respectively, at 1 kHz using the second imputation method; 1.04 (0.86-1.24), 1.14 (0.91-1.43), 1.13 (0.83-1.54), 1.45 (0.96-2.19), and 1.35 (0.82-2.23), respectively, at 4 kHz using the first imputation method; and 1.03 (0.86-1.24), 1.17 (0.95-1.44), 1.15 (0.87-1.53), 1.54 (1.06-2.24), and 1.44 (0.88-2.35), respectively, at 4 kHz using the second imputation method. In conclusion, higher systolic blood pressure was associated with hearing impairment at 1 kHz. No clear association was observed at 4 kHz.

Effects of primary arterial hypertension on cochlear function

BACKGROUND

Hypertension (HT) is one of the most common chronic diseases. The existing literature on HT and hearing contains conflicting results, and no consensus has been reached yet.

OBJECTIVES

This study aimed to investigate cochlear function in hypertensive and normotensive groups.

METHODS

This study was conducted on 34 patients with primary HT and 17 healthy adults. The Cochlear function was assessed with conventional audiometry (0.125-8 kHz), ultra-high frequency audiometry (10-16 kHz), the transient evoked otoacoustic emission (TEOAE) test, and the distortion product otoacoustic emission (DPOAE) test.

RESULTS

Hearing thresholds at 8, 10, 12.5, 14, and 16 kHz were significantly poorer in the HT group than in the control group (p < .05). There was no significant difference in the mean conventional thresholds between the groups. Compared to the control group, the patient group exhibited statistically significant lower amplitudes of TEOAE and DPOAE.

CONCLUSION

This study demonstrated significantly poorer high-frequency hearing and lower otoacoustic emission amplitudes for adults with HT. Impairment in hearing thresholds associated with HT begins at ultra-high frequencies in the cochlea. HT may be a potential risk factor for the development of hearing loss; therefore, individuals with HT should be screened for auditory function.

Association between a High-Potassium Diet and Hearing Thresholds in the Korean Adult Population

The aim of this study was to determine and evaluate the association between potassium intake and hearing thresholds in the Korean adult population. Data from the Korean National Health and Nutrition Examination Survey were analyzed. Participants were divided into tertiles on the basis of their potassium intake as follows: low, middle, and high. Pure-tone audiometry was performed using an automated audiometer. We calculated as the average threshold at the low-frequency pure-tone average (0.5 and 1 kHz), mid-frequency pure-tone average (2 and 3 kHz), and high-frequency pure-tone average (4 and 6 kHz). The average hearing threshold (AHT) was calculated as the pure-tone average of the thresholds at 0.5~3 kHz. Hearing loss (HL) was defined as an AHT of >40 dB in the better ear. There were 1975 participants each in the low, middle, and high tertile groups. The four different average hearing thresholds significantly decreased with an increase in the potassium intake tertile. Multivariate analysis revealed that the four different average hearing thresholds were significantly lower in the high tertile group than in the other two groups. In addition, univariate and multivariate linear regression analyses showed that the potassium intake level was inversely associated with each of the four different average hearing thresholds. Analyses of participants matched based on propensity scores and participants not matched based on propensity scores yielded similar results. The results of this study suggest that high potassium intake levels were associated with a lower prevalence of HL and lower hearing thresholds in the Korean adult population.

Auditory responses in a rodent model of Attention Deficit Hyperactivity Disorder

A central component of Attention Deficit Hyperactivity Disorder (ADHD) is increased distractibility in response to visual and auditory stimuli, which is linked to the superior colliculus (SC). Furthermore, there is now mounting evidence of altered collicular functioning in ADHD and it is proposed that a hyper-responsive SC could mediate symptoms of ADHD, including distractibility. In the present study we conducted a systematic characterisation of the intermediate and deep layers of the SC in the most commonly used and well-validated model of ADHD, the spontaneously hypertensive rat (SHR), building on prior work showing increased distractible behaviour in this strain using visual distractors. We examined collicular-dependent orienting behaviour, local field potential (LFP) and multiunit activity (MUA) in response to auditory stimuli in the anaesthetised rat, and morphological measures, in the SHR in comparison to the Wistar Kyoto (WKY) and Wistar (WIS). We found no evidence of increased distractibility in the behavioural data but suggest that this may arise due to cochlear hearing loss in the SHR. Furthermore, the electrophysiology data indicate that the SC in the SHR may still be hyper-responsive, normalising the amplitude of auditory responses that would otherwise be reduced due to the hearing impairment. The morphological measures of collicular volume, cell density and ratios did not indicate this potential hyper-responsiveness had a basis at the structural level examined. These findings have implications for future use of the SHR in auditory processing studies and may represent a limitation to the validity of this animal model.

Hypertensive retinopathy and sensorineural hearing loss

OBJECTIVE

To determine the correlation between hypertensive retinopathy (which is the end-organ damage of the vessels due to chronic hypertension) with sensorineural hearing loss.

METHODS

Pure tone hearing threshold of 56 hypertensive patients were compared with 56 normal age and sex matched control. Comparisons of pure tone hearing threshold are made among different group (grade) of hypertensive retinopathy patients and control (non-hypertensive patients).

RESULTS

The mean hearing thresholds were higher (worse) in all the frequencies on both sides in the hypertensive study group compared with normal subjects. However it was found to be statistically significant when tested using independent sample test (p < 0.05) on right ear at 2,000 Hz, 4,000 Hz and 8,000 Hz only. The mean hearing threshold is higher in all frequencies in the presence of retinopathy compared to control. However, the difference was found to be only statistically significant in the mean hearing threshold between grade I and control at 4,000 Hz and 8,000 Hz on both sides and at 1,000 Hz and 2,000 Hz on right ear. Hypertensive patient with grade I retinopathy had higher pure tone hearing thresholds at 4,000 Hz and 8,000 Hz compared to hypertensive without retinopathy and normal control.

CONCLUSIONS

Hypertensive retinopathy appears to be associated with high frequency sensor neural hearing loss.

Risk factors in the genesis of sensorineural hearing loss in Finnish forestry workers

A detailed analysis of risk factors for the development of sensorineural hearing loss (SNHL) was carried out in 199 forest workers. The hearing threshold of both ears at 4000 Hz was measured, and the effect of age, exposure to noise, blood pressure, presence of vibration induced white finger (VWF), tobacco smoking, plasma LDL-cholesterol concentration, and consumption of drugs were evaluated by multiple linear regression analysis. Aging was the major risk factor, followed by exposure to occupational noise and the presence of VWF. Plasma LDL-cholesterol concentration and the use of antihypertensive drugs also correlated significantly with SNHL. These main factors were able to explain about 28% of the SNHL variance. Additional factors in the analysis, including smoking, systolic and diastolic blood pressure, and consumption of salicylates did not significantly contribute to the genesis of SNHL.

Evaluation of factors affecting sensory neural hearing loss

A detailed analysis of risk factors in the development of sensory-neural hearing loss (SNHL) was carried out in 199 forest workers. The mean hearing threshold of both ears at 4000 Hz was measured and the effect of age, exposure, blood pressure, presence of vibration induced white finger (VWF), tobacco smoking and plasma lipid concentrations on SNHL were evaluated by multiple linear regression analysis. A part of aging the major risk factors were presence of VWF, elevation of LDL-cholesterol level and usage of antihypertensive agents. Additional factors in the analysis, e.g. smoking and diastolic and systolic blood pressure did not significantly contribute to the genesis of SNHL.

Comparative morphometric analysis of cochlear vessels in Wistar-Kyoto rats, spontaneously hypertensive rats, and aged spontaneously hypertensive rats

Vessel density and the ratio of the tissue area to the vessel surface area were studied by morphometric analysis techniques in normal rats, spontaneously hypertensive rats (SHR), and aged spontaneously hypertensive rats (aged SHR). Horseradish peroxidase was injected intravenously and the animals were killed 10 minutes later. The temporal bones were harvested, fixed in glutaraldehyde, and decalcified in 10% ethylenediamine tetraacetic acid (EDTA). After 7 days of decalcification, the cochleas were dissected and incubated with a diaminobenzidine tetrahydrochloride solution. Sections with stained vessels were projected onto the digitizing plate with the help of the camera lucida. The computer was used to calculate tissue area, vessel length, and vessel surface area. A statistically significant increase (p less than 0.05) in both the tissue area to vessel length ratio and the tissue area to vessel surface area ratio was demonstrated in the SHR and the aged SHR groups when compared to the WKY in the stria vascularis. No statistically significant difference was found between the two SHR groups. These data show a decrease of the vessel density in the capillary beds of the stria vascularis in spontaneously hypertensive rats. No statistically significant difference was found in the diameters of the capillary among the three groups.

Cochlear blood flow in relation to age in normotensive and spontaneously hypertensive rats

Cochlear blood flow was studied with the microsphere method in young and old normotensive and spontaneously hypertensive rats. The young animals were 3-6 months old and the old ones 18-24 months. The cochlear blood flow in young rats was 1.64 microliter/min/cochlea for the normotensive and 1.51 for the spontaneously hypertensive rats. In the old rats, the cochlear blood flow rates were 1.40 and 1.29 microliter/min/cochlea, respectively. The differences were not significant between the age groups, nor between the normotensive and spontaneously hypertensive rats. However, there was a tendency towards lower cochlear blood flow with increasing age, especially among the spontaneously hypertensive rats. The difference between young normotensive and old spontaneously hypertensive rats was significant (p less than 0.05). The group of old hypertensive rats was also the only one with evident morphological changes in the organ of Corti.

Sensory-neural hearing loss during combined noise and vibration exposure. An analysis of risk factors

A detailed analysis of risk factors for the development of sensory-neural hearing loss (SNHL) was carried out on 122 forest workers. These forest workers were selected from a larger group (n = 217) by restricting the age range to 30-55 years. The hearing threshold of the left ear at 4000 Hz was measured and the effect of age, exposure, systolic and diastolic blood pressure (DBP), presence of vibration-induced white finger (VWF), tobacco smoking and use of earmuffs were evaluated in multiple linear regression analysis. Robinson's nonlinear model was used to evaluate the rate of hearing loss. Aging was the major risk factor and it explained 15.4% of the variance of the SNHL. The presence of VWF was the second most important single risk factor and explained a further 5.2% of the SNHL. Elevation of DBP correlated significantly with SNHL and explained an additional 4.1% of the SNHL. These main factors were able to explain about 26% of the spread of SNHL. Additional factors in the analysis, e.g. smoking, systolic blood pressure, did not significantly contribute to the genesis of SNHL. When Robinson's model was applied to the SNHL data, on a group basis, we did not observe any exaggerated risk of hearing loss due to combination of noise and vibration. In combined exposure subjects with VWF as well as subjects with enhanced DBP will run a higher risk for SNHL.

The site of involvement of hypertension within the cochlea. A comparative study of normotensive and spontaneously hypertensive rats

The function and morphology of the cochlea of the spontaneously hypertensive rat (SHR) were examined and compared with the age-paired normotensive Wistar Kyoto rat (WKY). Electro- cochleographic study revealed that the function of the cochlea in the SHR declined with increasing age to a greater extent than that of WKY. Electronmicroscopic study revealed that the primary site of the cochlear deterioration of the SHR was the vascular stria, followed by the organ of Corti. Some hypotheses to explain this phenomenon are proposed for further study.